1. Field of the Invention
The present invention relates to a receiver for receiving a high definition signal, and more particularly, to an automatic gain control circuit of a high definition TV (hereinafter, HDTV) receiver and a method therefor.
In general, in a radio frequency (RF) signal transmitted from a transmitter, the amplitude of a signal is changed by various channel circumstances during transmission and is received by a receiver. In an automatic gain control (hereinafter, AGC) circuit, the amplitude of a received signal with severe changes in the amplitude is uniformly controlled to a predetermined level, which is critical for a digital signal processing system. When the amplitude of the received signal changes, it is not possible to reproduce the original signal since appropriate demodulation is difficult to perform in the receiver.
2. Description of the Related Art
Meanwhile, a conventional AGC circuit used for an RF receiver having a digital signal processor is provided in U.S. Pat. No. 5,451,948. In the conventional AGC circuit provided in the above-mentioned patent, a sampling clock corresponding to a frequency of more than two times an intermediate frequency (IF) signal is required during an analog-to-digital (A/D) conversion since the IF signal is used. Therefore, when the AGC circuit is realized, an expensive device with a very fast operation speed must be used. Also, timing must be correctly adjusted when a front-end AGC signal is forwarded to a back-end AGC loop and an AGC operation is not stable since an input signal is used. In particular, the AGC circuit is minimally effective when it is applied to a GA-HDTV (Grand Alliance-HDTV) system due to the characteristics of a vestigial sideband (VSB), the transfer signal standard of the GA system.